This application is based on Application No. 2001-115250, filed in Japan on Apr. 13, 2001, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an abnormality detecting apparatus and method for detecting abnormality in a position detection device, which is applicable for both rotational position detection and linear position detection, including a rotational position detector such as a position detecting resolver, a position detecting synchronizer, etc., and a linear position detector utilizing position detection principles similar to those for rotational position detection. More specifically, it relates to abnormality determination and processing in such a position detection device in an electrically operated or motorized power steering system for assisting an operator""s steering effort exerted on a steering wheel by means of an electric motor.
2. Description of the Related Art
In the past, a resolver, a typical one of such kinds of position detectors, has been employed for rotational position detection in which output signals from two orthogonally arranged winding members are input to a resolver digital converter (hereinafter simply referred to as R/D converter). By the use of this position detection device, a motor for a motorized power steering system is controlled to rotate.
An example of such a resolver is illustrated in FIG. 11. In FIG. 11, the resolver 10 has a single primary winding member to which an excitation signal (sin xcfx89t) 14, which is a sine wave voltage for excitation of the resolver, is input from an oscillation circuit 12. The resolver 10 also has two secondary winding members arranged in a mutually orthogonal relation with respect to each other to output induction signals 16, 18, which are generated, for example, by amplitude modulating the excitation signal 14 with cos xcex8 and sin xcex8, respectively, in accordance with the rotational position xcex8 of the motor of the motorized power steering system. Hereinafter, the output signal of the secondary winding members generated through amplitude modulation with cos xcex8 is referred to as a cos signal 16, and the output signal of the secondary windings generated by amplitude modulation with sin xcex8 is referred to as a sin signal 18. These two output signals 16 and 18 are input to the R/D converter 20 which then generates a digital signal representative of the detected rotational position xcex8. The digital signal of this rotational position xcex8 is input to a control section 22 for use in the prescribed control.
When there takes place a break in the resolver, there might be caused malfunctions of various control mechanisms, and hence such a break has to be detected promptly. To detect abnormality in the resolver, there has conventionally been implemented a method of individually detecting the excitation signal 14, the cos signal 16 and the sin signal 18, respectively. In addition, another method of simultaneously detecting breaks in signal lines for these three signals has also been proposed. This method is advantageous in that simultaneous detection of breaks in the three lines serves to reduce the number of component elements and provide inexpensive broken-line detection as compared with the aforementioned individual broken-line detection method. An exemplary method of simultaneously detecting breaks in three lines is disclosed, for instance, in Japanese Patent Application Laid-Open No. 3-78668. FIG. 12 illustrates the construction of a conventional position detecting apparatus for simultaneous detection of breaks in three lines. In FIG. 12, two excitation signals supplied to a resolver 102 from an oscillation circuit 100 are gain adjusted into signals Vsin xcfx89 by means of an amplifier 104, which are then input to a full-wave rectifier circuit 106 wherein they are full-wave rectified into a DC voltage. The output signal of the full-wave rectifier circuit 106 is input to a comparator or comparison circuit 108. Also, a sin signal 18 output from the resolver 102 is gain adjusted into a signal Vsin xcex8 sin xcfx89t by means of an amplifier 110, which is then input to a phase shift circuit 112 where the signal Vsin xcex8 sin xcfx89t is phase-shifted, by phase-shifting sin xcfx89t, into a signal Vsin xcex8 cos xcfx89t which is in turn output therefrom to an addition circuit 114.
On the other hand, a cos signal 16 output from the resolver 102 is gain adjusted into a signal Vcos xcex8 sin xcfx89t by means of an amplifier 116, which is then input to the addition circuit 114. In the addition circuit 114, the signals Vsin xcex8 cos xcfx89t and Vcos xcex8 sin xcfx89t are summed to provide a combined signal Vsin(xcfx89t+xcex8) as its output. Since this signal Vsin(xcfx89t+xcex8) shifts by a phase xcex8 from the excitation signal Vsin xcfx89t, when full-wave rectified into a DC voltage by means of a full-wave rectifier 118, it provides the same DC signal as the output of the full-wave rectifier circuit 106. Then, the output of the full-wave rectifier 118 is also input to the comparison circuit 108, where the output voltage of the full-wave rectifier circuit 106 and the output voltage of the full-wave rectifier circuit 118 are compared with each other for determination of a break in the resolver 102. When a break is generated in the resolver 102, the output DC voltages from the two full-wave rectifier circuits 106, 118 become unequal whereby the break of the resolver 102 can be detected.
In the conventional abnormality detection apparatus for the position detection device as constructed above, the full-wave rectifier circuits each of a complicated construction are needed, thereby increasing the number of component elements and hence the cost of manufacture as well. Moreover, for example, in the event that the resolver is rotating with the signal line for the sin signal being broken, it is determined that the resolver is normal at a rotational position or angle of 0 or 180 degrees, and abnormal at all the other rotational positions or angles. Therefore, determinations of normality and abnormality are repeated, thus making it impossible to definitely determine the abnormality of the resolver.
The present invention is intended to obviate the above-mentioned problems, and has for its object to provide an abnormality detecting apparatus and method for a position detection device which is capable of performing abnormality detection with improved accuracy at low costs by detecting abnormality based on a peak value of a phase-modulated signal obtained corresponding to the rotational position of a rotating element such as a motor, the rotational position of which is to be detected.
Bearing the above object in mind, according to one aspect of the present invention, the invention resides in an abnormality detection apparatus for a position detection device in which at least one excitation signal having a predetermined periodic waveform is supplied to primary winding of a position detection sensor to thereby generate at least one output signal in the form of a phase modulated signal corresponding to a rotational position of a rotating member from secondary winding of the position detection sensor directly or after having been subjected to phase shifting and arithmetic operations, said apparatus comprising an abnormality detection section for determining an abnormality of said position detection device when said phase modulated signal has a peak value which is outside a predetermined range.
In a preferred form of the present invention, the abnormality detection section comprises: a peak hold circuit for detecting a peak value of said phase modulated signal and holding it for a predetermined period of time; and an abnormality detection determination processing section for determining abnormality when the peak hold value of said peak hold circuit is outside a predetermined range.
In another preferred form of the present invention, the peak hold circuit comprises a capacitor for setting a time constant, which is used for holding said peak value of said peak hold circuit, to a value sufficiently greater than a period of said phase modulated signal.
In a further preferred form of the present invention, the peak hold value of said peak hold circuit is input directly to said abnormality detection determination processing section.
In a yet further preferred form of the present invention, the abnormality detection determination processing section outputs a reset signal for resetting the peak hold value of said peak hold circuit.
In a still further preferred form of the present invention, the abnormality detection section comprises an abnormality detection determination processing section which, by means of software processing, takes in said phase modulated signal, calculates a peak value of said phase modulated signal and determines abnormality when said peak value is outside a predetermined range.
In a further preferred form of the present invention, the abnormality detection determination processing section is provided alone.
In a further preferred form of the present invention, said abnormality detection determination processing section is built in a control element which controls an object of which position is to be detected.
In a further preferred form of the present invention, said abnormality detection section determines an abnormality of said position detection device when the condition in which said peak value or peak hold value is outside a predetermined range continues for a predetermined period of time.
In a further preferred form of the present invention, said abnormality detection section counts the number of accumulative occurrences of the condition in which said peak value or peak hold value is outside a predetermined range, and determines an abnormality of said position detection device when said number of accumulative occurrences thus counted becomes equal to or greater than a predetermined value.
In a further preferred form of the present invention, an object of which position is to be detected by said position detection sensor is a motor for assisting a steering effort of an operator, and said position detection sensor detects a rotational position of said motor, and when said abnormality detection section determines an abnormality of said position detection device, a control unit with a motor drive circuit for driving said motor in a controlled manner operates to stop control for driving said motor thereby to prohibit motor driving.
In a further preferred form of the present invention, in said position detection device, said primary winding of said position detection sensor comprises a single primary winding member; said secondary winding of said position detection sensor comprises two secondary winding members arranged in an orthogonal relation with respect to each other; and an excitation signal having a predetermined periodic waveform is supplied to said single primary winding member whereby signals respectively induced in said two mutually orthogonal secondary winding members are subjected to phase shifting and arithmetic operations so as to cancel their unnecessary portions with each other thereby to provide a phase modulated signal corresponding to the rotational position of said rotating member.
In a further preferred form of the present invention, in said position detection device, said primary winding of said position detection sensor comprises two primary winding members arranged in an orthogonal relation with respect to each other; said secondary winding of said position detection sensor comprises a single secondary winding member; and two excitation signals having waveforms with a phase shift of 90 degrees relative to each other are supplied to said two mutually orthogonal primary winding members, whereby a phase modulated signal corresponding to the rotational position of said rotating member is induced in said single secondary winding member.
According to another aspect of the present invention, the invention resides in an abnormality detection method for a position detection device in which at least one excitation signal having a predetermined waveform is supplied to a primary winding side of a position detection sensor whereby a secondary winding side of said position detection sensor generates at least one output signal in the form of a phase modulated signal corresponding to a rotational position of a rotating member directly or after having been subjected to phase shifting and arithmetic operations, said method comprising step for determining an abnormality of said position detection device when said phase modulated signal has a peak value which is outside a predetermined range.
The above and other objects, features and advantages of the present invention will become more readily apparent to those skilled in the art from the following detailed description of preferred embodiments of the present invention taken in conjunction with the accompanying drawings.